I am designing protocol to share a random generated n long password between k parties using Shamir's Secret Sharing. I know that share alone does not reveal much information about the original password to the attacker except for the size of password. My solution now is to extend each password to 512 bits using constant pattern.
How secure is this against brute-force attack when attacker has t-1 shares and knows the stretching pattern? Is there any better way to obfuscate the original password size? Would it be better to encrypt the password with symmetric cipher let's say AES256-CTR and random key K and then split that key with SSS algorithm?